The majority of the gram-positive, non-spore-forming, anaerobic bacilli isolated from clinical material are which organism?

• A. Bifidobacterium dentium
• B. Propionibacterium acnes
• C. Capnocytophaga ochracea
• D. Eubacterium limosum

Answer: (B)

Propionibacterium acnes is a common inhabitant of human skin and is a Gram-positive, non-spore-forming anaerobic rod. In clinical microbiology, samples collected from skin, devices, or blood cultures often yield this organism because it is part of the normal skin flora and can contaminate specimens during collection. Its presence as a slow-growing anaerobic Gram-positive bacillus makes it the most frequently encountered among this group in routine clinical material, even though it is sometimes a true pathogen in prosthetic device or deep-seated infections.

The other organisms listed are less representative of this group in routine isolates: one is a Gram-negative rod, and the others are less typically recovered as common skin-associated anaerobic Gram-positive bacilli in clinical cultures.